There is a wide range of apparatus (e.g. scrubbing towers, fractionation towers, rectifying towers) in which liquid and vapors counterflow through interstices of packing material to establish a relatively large area of contact between the two resulting in desired mixing. As well as providing an extended surface area, the packing material also acts as a means for controlling the flow rate and thus the contact time of the liquid with the gas or vapor. Such equipment is typically arranged in vertical towers or columns in which a plurality of separate beds may be provided, each bed including packing material with the liquid moving downwardly for desired mixing with the counterflowing gas or vapor.
A persistent difficulty, especially where the column is of relatively large size, is that of maintaining a uniform flow of liquid, and to a lessor extent, vapor across the column cross-section. For example, there is a tendency for liquid to work to the outside of the tower and to flow downwardly along the column inner wall, leaving the packing central portions relatively untouched by the liquid. Liquid migrating to the tower wall in this way also results in additional pressure loss of the upwardly flowing vapor due to direct contact with the packing material. Both of these actions serve to reduce the contact efficiency between the liquids and vapors and thereby the column efficiency.
The prior art has recognized for some time the need for good liquid distribution in a packed column or tower. Note, for example, Hoftyzer, Trans, Instn. Chem. Engrs. v. 42,T109 (1964); and Ross, Chem. Engr. Progress, v. 61 10,77 (1965). More recently, with the development of better distributors and better packings the prevalent opinion, until conception of the present invention, has been that with careful attention to initial liquid distribution it is possible to design for packing beds of 25 to 30 feet between redistributors. Chemical Engineers' Handbook, 6th Edition, Sec. 18, page 29 (1984). However, the distribution and redistribution referred to is solely that of the liquid.